Pollution control system for kiln exhaust

ABSTRACT

Disclosed is a method and apparatus for the reduction of organic compounds and other emissions from an industrial plant utilizing a cement or minerals kiln that has a high level of organic compound emissions. The invention consists of a filter for the control of particulate emissions which has been treated with a catalyst to provide catalytic destruction of gaseous emissions as process gases are passed through the porous medium of the filter.

BACKGROUND OF THE INVENTION

There is an increasing level of awareness concerning the emission ofcertain volatile organic compounds (VOCs), combustion byproducts such ascarbon monoxide and NO_(X), and dioxin/furans from industrial plantssuch as cement manufacturing facilities. With this heightened level ofawareness, more stringent environmental regulations are being adopted toensure low emissions from these industrial plants. In some cases, thelevel of emissions currently experienced may not be adequately reducedusing existing technologies in order to meet new environmentalregulations. In other cases, existing technologies for emissionscontrols in other applications are prohibitively costly in industrialapplications. Consequently, there is an interest in developing newsystems for controlling these high levels of emissions to meet newlyproposed regulations, and that is an object of the present invention.

Very few cement and lime kilns have installed specialized controls foremissions of organic compounds. Cement kilns in the United States haveattempted the use of Regenerative Thermal Oxidizers (RTOs), such asthose devices described in U.S. Pat. No. 5,352,115 and U.S. Pat. No.5,562,442. These devices subject the process gases to intense oxidizingconditions produced by applying a direct heat source and introducing airto the system in order to incinerate the organic compounds in the gasstream. The exhaust gases are heated to a temperature in excess of 800°C., and much of this heat is recovered through the system and used forpreheating the gas stream prior to the combustion region. The devicesrequire a clean fuel for heating, as soot and ash introduced from thefuel can reduce the thermal efficiency of the unit. These devices are oflimited applicability in use with cement and minerals processing systemsfor several reasons—they are small in size relative to the process gasstream that must usually be treated (requiring multiple, parallelunits), the intense oxidizing conditions produced in the unit canoxidize SO₂ present in the gas stream to SO₃ (which necessitates the useof a wet limestone scrubber or other SO₂ control device prior to theRTO), and the use of additional fuel firing for operation will increaseemissions of carbon monoxide and carbon dioxide. Combined, thesedisadvantages make RTOs very difficult to install in industrial plantssuch as cement kilns because of the large space required for the RTO andsupporting equipment, the high cost of installation, and the high costof operation.

An alternative approach that may be attempted is the use of catalyticmeans of the destruction of organic compounds and carbon monoxide.Catalyst applications in cement kiln systems have generally beentargeted towards the removal of nitrogen oxides through “SelectiveCatalytic Reduction”, but the art of using catalysts in similarapplications for the removal of organic constituents may also bepracticed, as in U.S. Pat. No. 6,156,277. In this method, the exhaustgas from a cement kiln is directly passed through a reduction catalystfor the destruction of the emissions from the kiln system. Thetemperatures required for the chemical reactions for the destruction ofNOx and other emissions products is generally between 250° C. and 450°C. in practice, although wider temperature ranges are available withspecific designed catalysts. In a typical cement kiln process, theexhaust gas from a preheater/precalciner system is typically in such arange. While this temperature range is conducive to a high activity forthe catalyst, these systems often see issues associated with the loadingof particulate matter in the exhaust gas stream. Typical dust loadingsin these gas streams may be in the range of 20 to 50 grams ofparticulate per cubic meter of exhaust gas, although dust contentsexceeding 150 grams of particulate per cubic meter of exhaust gas can beseen. The particulate matter is typically comprised of the fine dustfraction of feed material introduced to the kiln system which is notcompletely captured within the kiln or preheater system. This fine dustis comprised of varying amounts of and compositions containing calcium,aluminum, silica, and iron, as well as sodium, potassium, chlorides,sulfur and minor constituents such as phosphorous, arsenic, thallium,and zinc. Depending on the catalyst structure in use, any of thesecompounds can cause degradation of the catalytic effect of the systemthrough de-activation of the surface, poisoning of the catalyst, erosionof the catalytic surface, or the blocking of the catalyst surface fromcontact with the gaseous constituents. In addition, the dust content ofthe gas stream requires larger openings in the catalytic structures inuse in these systems, requiring larger catalyst structures to obtain thesame catalytic surface as is found in other industrial applications. Insystems where SCR is practiced, soot blowers for dedusting and periodiccleaning of the catalyst surface are required. The loss in efficiencyassociated with dust loading therefore leads to higher costs for thesesystems for design and operation than in comparable industries with lowdust loads.

As an improvement over these “high dust SCR” applications, systems havebeen proposed which include a step for removal of the dust present inthese industrial applications prior to the catalyst structure. Thesesystems comprise an additional cleaning step utilizing a dust filter ora precipitator prior to the catalytic structure, such as is described inUS Application 2010/0307388. In this arrangement, the gases coming froma cement kiln system are first passed through a dust precipitationsystem to remove particulate matter. The gases are then passed throughthe reduction catalyst for destruction of the targeted pollutants. Aftertreatment in the reduction catalyst, the hot gases may then be used inother devices found in the industrial facility, such as grinding mills,and vented through a stack. This “low dust SCR” arrangement offersseveral advantages over the “high dust SCR” arrangement, including alonger lifetime for catalyst structures before replacement, the usage ofsmaller openings between catalyst plates or honeycombs which allows fora smaller and less costly catalytic structure, and lower operating costsassociated with less replacement of catalyst. This arrangement does comewith several disadvantages. The requirement for a dust collection devicesuch as a filter or precipitator is an added piece of process equipmentthat comes with installation and long term operating and maintenanceexpenses. The additional pressure drop through the precipitator orfilter, in addition to the catalyst structure, will increase the powerrequirements on any fans utilized for drafting gas through the overallsystem. In addition, the layout requirements of the cement kiln orminerals processing facility will often make it difficult or impossibleto fit both the filter or precipitator and a catalytic structure withinthe confines of available areas for installation.

In view of the prior art issues, the objects of the present inventioninclude improving the control of various undesirable emissions fromcement and minerals, and obtaining a high efficiency of catalyticactivity such as is found in a “low dust SCR” applications while havinga high inlet dust loading similar to that encountered in “high dust SCR”applications, while utilizing fewer pieces of equipment and a lowerpressure drop than a “low dust SCR” system.

BRIEF DESCRIPTION OF THE INVENTION

The above and other objects are achieved by utilizing a device fittedwith a filter element or filter elements which are pretreated with thecatalyst or composed of the catalytic materials dispersed through thefilter elements.

According to the invention, there is a method for the reduction oforganic compounds and other emissions from an industrial plant having acement or mineral kiln or calciner system that has a high level ofemissions. The invention treats the exhaust gas stream from the cementor minerals processing plant on a filter medium in order to removeentrained particulate, and destroys the targeted pollutant within thestructure of the filter medium. Particulate captured on the surface ofthe filter medium is periodically removed from the surface of the mediumto prevent blockage of the porous filter medium and to avoidundesireable increases in energy consumption at the processing plant.Such removal can be achieved by a number of methods, includingsubjecting the filter medium to sonic or ultrasonic vibration or themechanical removal of particulate matter with a solid object.Pre-treatment of the exhaust gas stream can be used to enhance thepollutant destruction capabilities of the filtration device, or toprevent oxidation of entrained pollutants to less desirable compounds.This invention is not limited to cement or lime plants. It can be usedin any industrial processing plant where the emission of organiccompounds, total organic carbons or volatile organic carbons, carbonmonoxide, nitrogen oxides, or dioxin/furans require a very high degreeof treatment for attainment of regulatory requirements, such as, forexample, in plants that use long dry cement kilns, short cement kilnswith precalciners, and lime kilns.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a plant for the production of cement clinkeradapted to the cleaning of hydrocarbons and other contaminants accordingto the invention.

FIG. 2A is a diagram of one embodiment of the invention in a cement orminerals kiln system.

FIG. 2B is a more detailed view of a filter element utilized in theinvention.

FIG. 3 is a diagram of another embodiment of the invention utilizing adifferent method for holding and supporting the catalytic filterelements.

FIG. 4A is a diagram of another embodiment of the invention utilizinganother method for holding and supporting the catalytic filter elementsand for removal of the collected particulate matter.

FIG. 4B is an isometric view of the embodiment of the invention depictedin FIG. 4A.

FIG. 5 is another general diagram of a plant for the production ofcement clinker adapted to the cleaning of hydrocarbons and othercontaminants according to the invention.

FIG. 6 is an example of organic compound reduction curves comparingremoval efficiencies of the invention at varying temperatures and forvarious organic compounds.

DESCRIPTION OF THE INVENTION

Although the invention is particularly directed to the reduction inemissions of organic compound emissions, the present invention alsoapplies to the removal of other products of incomplete or partialcombustion such as carbon monoxide, condensable VOC's, nitrogen oxides,and dioxin/furans that contaminate manufacturing processes. Many of theorganic compounds that this invention is directed towards fall undernumerous overlapping categories of compounds, such as Total OrganicCarbon (TOC), Total Hydrocarbons (THC), and Volatile Organic Compounds(VOC), and this invention is broadly aimed to the various compoundswhich are classified under these general categories. Also, whileemphasis is placed on a cement manufacturing process, the presentinvention is applicable to other minerals and kiln manufacturingprocesses, such as lime manufacturing processes and other industrialprocesses where very high starting emission levels of these contaminatecompounds can not be sufficiently controlled using existing methods, orwhere existing methods of control are cost prohibitive.

Emissions of organic compounds from industrial process may originatefrom a variety of different sources within a system. In mineralsprocessing systems such as cement kilns, these sources may includeincomplete combustion of fuels fired within the system, decomposition orpartial combustion of organic species within feed components,contamination of gas streams with organic materials such as fromoiled-compressors, introduction of organic components in process waterused for cooling, and from introduction of ambient air which may containorganic components in small quantities. Also, the oxygen concentrationsat the exhaust of many industrial processes such as cement kilns arekept low in order to improve efficiencies within the systems, but suchlow oxygen concentrations inhibit full combustion of these variousorganic compounds prior to release from the system. These minorcomponents may contribute to localized conditions such as smog, and aretherefore seeing increased levels of regulation.

The invention in part comprises the use, in conjunction with a kilnexhaust, of a device fitted with a filter element or filter elementswhich are pretreated with the catalyst or composed of the catalyticmaterials dispersed through the filter elements. The catalyst utilizedin the pretreatment or the construction of the filter element is chosenprior to installation of the filter elements within the device in orderto treat those gaseous emissions within the exhaust stream from theindustrial process which must be controlled in order to achieveregulatory compliance. While the catalysts are designed for the controlof organic compound emissions such as Volatile Organic Compounds (VOC),Total Hydrocarbons (THC), Total Organic Carbon (TOC), and similarclassifications of emissions, the catalyst for the pretreatment of thefilter elements or the dispersal through the filter elements may also bechosen for the reaction or destruction of other compounds includingdioxins, furans, carbon monoxide, or oxides of nitrogen (NO_(X)), or canbe used for the oxidation of mercury for further treatment and captureafter the device. The catalytic elements used in the treatment ormanufacture of the filter elements can contain a mixture of any ofvanadium, platinum, palladium, ruthenium, titanium, lanthanum, cerium,yttrium, zirconium, tungsten, manganese, niobium, molybdenum, nickel,iron and copper in compositions designed to remove those emissions whichmust be reduced in the gas stream.

The filter elements are porous membranes which allow for the passing ofexhaust gases through the elements, but of sufficiently small pore sizeto capture a significant quantity of the dust on the surface of theelements which is exposed to the process exhaust gas containingentrained dust. The surface of the filter element exposed to the processexhaust gas containing entrained dust is referred to as the “dirty side”of the filter element, while the surface of the filter opposite the“dirty side” and through which the dedusted process gases pass to theoutlet of the filter is referred to as the “clean side” of the filterelements. The filter element is comprised of the porous substrate aswell as the catalytic component of the filter element during themanufacturing process. The filter elements are treated with thecatalysts either in whole or in part, with catalysts deposited on boththe “clean side” surface and the “dirty side” of the filter elementpenetrating through a depth to the inside of the filter element, withthe maximum penetration of the catalysts being through the entirethickness of the filter element, i.e. from the “clean side” to the“dirty side” of the filter element. In all cases, it is preferred not tohave the catalysts applied only to the “dirty side” of the filterelement, as this exposes the catalyst to the dust particles which mayerode or “poison” the catalyst and reduce its lifetime. Thenon-catalytic portion of the filter element, which serves as a substrateto the catalyst and as the porous filter for entrained dust in the gasstream, is composed of a material which is designed to retain sufficientfiltering properties through the design range at which the filterelements will be exposed for filtration of dust and for catalyticreduction of gaseous pollutants. The non-catalytic composition of thefilter element may be comprised of any of porous ceramic, glass fibers,ground quartz, alumino-silicate ceramic fiber, rutile, calcite,corundum, kaolinite, and diatomaceous earth, among others.

The surface of the filter elements which is exposed to the processexhaust gas entering the device is periodically cleaned to preventexcessive accumulations of dust, which would otherwise increase thepressure drop of the device, and thus increase the power consumption ofthe system in operation. Cleaning of the device may be performed throughmechanical cleaning, such as scraping or “rapping” of the filterelements, but is preferentially performed through periodic “pulsing” ofgas counter to the flow of the industrial process exhaust gas enteringthe filter element. Dust which is released from the filter element maybe returned to the cement or mineral processing facility, or may bewithdrawn and stored for use elsewhere.

The filter element is placed such that the exhaust gases from the cementor minerals industrial process, which contain entrained particulatematter, are passed through its porous filter. The majority of theentrained particulate matter is captured on the surface of the filterelement and will not come into contact with the interior of the filterelement. Gases passing through the pores of the filter element come indirect contact with the catalytic compounds with which the element hasbeen treated, ensuring contact time between the gas and the catalyst.This reduces the required residence time with the catalyst and allowsfor the possibility of a smaller installation. By using the filterelements as the catalyst substrate, the steps of separation (of the dustfrom the gases) and catalytic contact may occur within the same device,also reducing the size and cost of an installation.

By suitable pretreatment or post treatment of the gases around thefilter device, additional pollutant controls may be achieved. In onevariant of the invention, a sorbent for sulfur emissions may be injectedbefore the device to capture sulfur dioxide emissions prior to thefilter elements and the catalyst. In this manner, the sulfur dioxide maybe captured prior to the gases contacting the catalyst, preventing thepotential formation of sulfur trioxide within the filter elementsthrough catalytic oxidation.

In one variation of the invention, a sorbent for capture of mercuryemissions is injected after the filter device in order to capturemercury emissions which have been oxidized in contact with the catalyst.

In one variation of the invention, a nitrogenated agent such as ammonia,urea, ammonium bisulfate, or flyash may be injected prior to the filterdevice in order to reduce NO_(X) emissions. For example, injection ofammonia may be placed immediately prior to the inlet of the filterdevice, or may be injected in excess within the industrial processproducing the exhaust gas with the resulting ammonia slip furtherreacting within the filter device.

Placement of the catalytic filter device into the industrial process isdependent upon the pollutants in the exhaust gas stream that are to bedestroyed. The activity of the catalyst and the selectivity of thecatalyst for destruction of gaseous emissions are dependent upon thetemperature of the gas stream. Organic compounds such as methanol can bedestroyed in large percentages even at temperatures as low as 120° C.,while organic compounds such as propane may require temperatures as highas 300° C. It is preferential for the destruction or reaction ofshorter-chain (less than 7 carbon atoms) hydrocarbons, of single-bonded(i.e. saturated) hydrocarbons, and NO_(X) emissions to place the deviceas close to the exhaust of the cement or minerals processing system asis possible in order to obtain a gas temperature in the range of 250 to400° C., and more preferentially 300 to 350° C. If the destruction orreaction of longer-chain hydrocarbons (7 or more carbon atoms), double-or triple-bonded (i.e. unsaturated) hydrocarbons, and/or cyclic oraromatic hydrocarbon compounds are desired, without need for highertemperatures for the treatment of other emissions through catalyticmeans, then the device may preferentially be used in the temperaturerange of 80° C. to 250° C., and more preferentially between 150° C. and200° C.

The catalytic activity of the filter elements may also be enhancedthrough the treatment of the gas stream with other means. These meanswould include the use of ozone, peroxide, potassium permanganate,calcium chloride, sodium hydroxide, or other oxidizing species injectedupstream of the filter element or within the filter device.

The invention is explained in greater detail below with the aid ofdrawings.

In the system of the present invention illustrated in FIG. 1, materialis treated in a kiln 1, which heats the material to undergo chemicalchanges. In cement kiln systems, the feed entering kiln 1 throughconduit 2 may first be preheated in a preheater system 50 comprising anumber of counter current heat exchangers 51 in the form of cyclones.The material may also pass through a calciner or pre-calciner 52 forremoval of carbon dioxide prior to entering kiln 1. Product from kiln 1is discharged into a material cooler 3 which serves the purpose ofcooling the kiln product before discharge 4, and of recuperating heatfrom the product to be returned to the kiln 1 or to the calciner 52.Cooling air is passed over the material and is heated before passingthrough the kiln hood 5 to enter kiln 1 or to enter the calciner 52through conduit 6. The air flowing to kiln 1 and calciner 52 is utilizedin combustion process. Excess air that enters cooler 3 for productcooling is directed to an exhaust vent 7. In typical arrangements, theair exiting cooler 3 through exhaust vent 7 are cooled in a heatexchanger 8, and entrained particulate matter is removed in a dustcollector 9 and removed as a product stream 10. The cooler excess airmay then be vented to atmosphere at 11, or used in other means withinthe process. Gases exiting from kiln 1 are directed through calciner 52and into preheater system 50. Feed material 20 to the system is directedto the preheater system 50 for thermal treatment, and may be splitbetween various counter current heat exchangers 51 for the control oftemperature from the exhaust gas 21 or for the high temperaturetreatment of the feed material. In the typical configuration, the feedmaterial is directed to the uppermost cyclone heat exchanger asdepicted. Emissions of organic compounds, mercury, and carbon monoxidefrom the thermal treatment of feed material 20 within preheater system50, and emissions of organic compounds, carbon monoxide, and otherproducts of incomplete combustion from the calciner 52 or kiln 1, willleave the system in the exhaust gas stream 21. Nitrogen oxides createdand mercury released from combustion processes in calciner 52 and kiln 1will also leave the system in the exhaust gas stream 21. The exhaust gasfrom the kiln system is then directed through the catalytic filtersystem 100 for the destruction or reaction of gaseous emissions inexhaust gas stream 21. After passing through the catalytic filter system100, treated exhaust gas stream 22 may be directed to a gas conditioningtower 23 which utilizes cooling water 24 for the cooling of the gasstream for further processing. Conditioned gas 25 from the gasconditioning tower 23 may be directed to a raw mill system 60 ormultiple mill systems, or to a main dust collector 70 for finalparticulate control. Raw feed materials 61 are introduced to the rawmill system 60 which grinds the feed materials to a size suitable forthe production of cement clinker. The product material from the millexits the mill 60 with an exhaust gas stream 65 and is separated in acollection device such as a cyclone 62 or cyclones. The material 63captured in the cyclone 62 is transported to a blending and/or storagesilo 90 for use in the kiln system. The gases 64 from cyclone 62 arethen directed to a main dust collector 70 for collection of fineparticulate matter not captured in the cyclone. The gases from the maindust collector may then be vented from the system 80. Material 71captured in the main dust collector is then transported to the blendingand/or storage silo 90, or to some other storage area for furthertreatment or disposal. Material blended and/or stored in silo 90 is usedas kiln feed 20 for the kiln system. If the kiln system utilizes a solidfuel for heating of material, hot gases may be removed from the system31 for use in a milling system for the solid fuel or for other heatingprocesses within the plant facility. The hot gases may alternatively beremoved from the system after the catalytic filter system and before thegas conditioning tower, or after the gas conditioning tower and beforethe main dust collector. Exhaust gases from the solid fuel grindingsystem may be returned to the system in a gas stream 41 prior to thecatalytic filter system, may be directly vented to atmosphere, or may becombined with the exhaust gases 80 from the main dust collector 70before being vented to the atmosphere.

The catalytic filter system 100 is depicted as being positioned betweenthe preheater/precalciner system and the gas conditioning tower, butdepending on the configuration of the kiln system and the requirementsfor gas flows for processing within the system, the catalytic filtersystem may alternatively be placed at a number of other locations withinthe system. For example, the catalytic filter system may be placed atlocation A (between the exit of the preheater system 50 and the hot gasstream 31 removed from the preheater exhaust gas stream 21), at locationB (between the hot gas stream 31 removed from preheater exhaust gasstream and the returned gas stream 41 from the solid fuel grindingsystem), or at location C (after the exhaust of the gas conditioningtower 23).

It may be preferred to utilize sorbents in the process prior to theposition of the catalytic filter system in order to capture items thatotherwise may oxidize to less preferable components in the catalyticfilter systems. Sorbents such as calcium oxide, calcium hydroxide orhydrated lime, trona, activated carbon, or proprietary sorbents such asMinsorb™ or Sorbacal™, may be utilized in this capacity in one or all oflocations S1, S2, and S3. The injection of additional reactive agentssuch as ozone, peroxide, potassium permanganate, calcium chloride,sodium hydroxide, or other oxidizing species, or ammonia, urea, or othernitrogenous compounds for conversion of emission components to thosemore readily destroyed within the catalytic filter system or to directlyimprove the destruction of compounds in the catalytic filter system maybe utilized in one or all of locations S1, S2, S3, S4 and S5.

FIG. 2A shows one embodiment of the present invention, with emphasis onarea 100 of FIG. 1. Process gases 101 from the exit of the kilninstallation, such as the exit of a cement kiln, preheater, orprecalciner system or a lime kiln or preheater system are directed via aconduit 102 to the catalytic filter unit 103. Filter unit 103 compriseshousing XXX, which encloses an interior portion of the unit which ispartitioned by a sheet 105 through which filter elements 104 areinserted. The filter elements are a porous material, such as afiberglass bag or a porous ceramic structure, which will allow theprocess gases to pass through, but which will trap a large portion ofparticulate matter on the surface of the filter element. It is preferredthat the porous filter will reduce the dust load of the gas passingthrough the filter element to 5 grams per cubic meter of process gas orless, preferentially less than 30 milligrams per cubic meter of processgas, and most preferentially less than 5 milligrams of particulate percubic meter of process gas. Particulate matter collected on the surfaceof the filter elements is removed from the surface of the filter andcollected in the bottom of the device at 106 and removed through awithdrawal system 107. Cleaning of the material on the surface may beconducted on a routine basis at set time intervals, or may be controlledby monitoring the accumulation of material on the filter element surfaceby means of a pressure monitoring device 108 to monitor the differencein pressures attained across the partition between the clean and dirtysides of the filter. Gases passing through the filter elements come intocontact with the catalytic material with which the filter elements havebeen treated or produced. Contaminants such as organic compounds reactupon the catalytic elements of the filter elements and are destroyed.The reaction activity of the catalyst to increase the reduction ofhydrocarbons present in the filtering element may be improved bycontacting the catalytic agents with a reactive agent, such as byinjecting one or more reactive agents at a point located prior to thecatalytic filter as described previously. The temperature of the gasstream is monitored at position 109 to ensure that the interior of thefilter device is maintained at a temperature that facilitates sufficientactivity of the catalyst, and if the temperature within the filterdevice is not suitable for the destruction of the targeted pollutant(s),process changes can be made prior to the catalytic filter to ensuresufficient temperature for efficient destruction of the entrainedpollutants. The temperature within the filter device can also becontrolled through the introduction of a gas stream 120 prior to thecatalytic filter system. Examples of gas streams for temperature controlinclude ambient air introduced by a fan or damper to reduce inlettemperature, hot gas streams from heat sources such as stand-by heaters,or waste heat from other areas of the cement or minerals processing kilnsystem such as from a cooler vent exhaust stream. While depicted asbeing located on the clean side of the filter elements at 109, thetemperature monitor can be placed on the dirty side of the filter, or inthe duct work prior to or after the catalytic filter.

The cleaned gases 110 exit the catalytic filter via a duct 111, and canbe used elsewhere in the process or vented to atmosphere.

FIG. 2B shows a more detailed view of a filter element 104. The gasstream with entrained particulate matter 152 impacts on the surface ofthe filter element adjacent to the filter elements 156. The gas streamfollows the direction of flow as shown by dotted line 151 and is forcedthrough the porous portion 150 of the filter element to come intocontact with catalytic agents container therein. The clean gas streamfrom which particulate matter has been removed passes to the “cleanside” 155 of the filter. The particulate matter 154 entrained in the gasstream is collected on the surface of the dirty side of filter elements104 and is removed periodically.

While the filter elements are depicted in FIG. 2A as being supported bythe partition within the catalytic filter, and the inlet gas entersbelow the partition and exits above the partition, multiple arrangementsof partition, filter elements, and gas inlets and outlets may beutilized depending on the possible layouts within the system and thematerials of construction used for the catalytic filter and the filterelements. By example, a porous ceramic filter element may be limited inlength by the strength of the filter element at the support point, whichmay necessitate a large number of filter elements to achieve sufficientparticulate matter control or catalytic activity. In this example, itmay be necessary to utilize a filter element which is supported frombeneath by the partition to allow for a greater strength in compressionthan is available in tension.

FIG. 3 depicts another embodiment of the system and method of thepresent invention in the context of a cement or minerals processing kilninstallation. Process gases 201 from the exit of the kiln installation,such as the exit of a cement kiln, preheater, or precalciner system or alime kiln or preheater system are directed via a conduit 202 to thecatalytic filter unit 203. The filter unit is partitioned by sheet 215and sheet 216 through which filter elements 204 are inserted. Thesupport provided to filter element 204 by sheet 215 is in tension, whilethe support provided to filter element 204 by sheet 216 is incompression. With, for example, a ceramic filter, as element 204 getslonger its weight becomes a concern at the support point. If such anelement is supported only from above a large shear stress can be createdon the element and it can crack at the support. It it's also supportedfrom below, the stress is in compression, which is easier for theceramic to accommodate without cracking. By distributing the support forthe element in this manner, a longer filter element may be used in thefilter device. By using a longer filter element, fewer elements may beused in the filter device. The longer elements will increase the heightof the filter device, but this can save on the length and width of thefilter device, which may be of critical importance when installing thefilter device in areas with other existing equipment.

Particulate matter collected on the surface of the filter elements isremoved from the surface of the filter and collected in the device 206and removed through a withdrawal system 207. Pressure monitoring device208 is used to monitor the difference in pressures attained across thepartition between the clean and dirty sides of the filter. Thetemperature of the gas stream is monitored at 209 The cleaned gases 210exit the catalytic filter via a duct 211.

FIG. 4A depicts another embodiment of the system and method of thepresent invention. Process gases 301 from the exit of the kilninstallation are directed via a conduit 302 to the catalytic filter unit303. The filter unit features a number of filter elements 304 supportedon a series of chambers or plenums 317 through which air passes from theinterior of the filter elements to the exterior of the filter device viaexit 311. Each plenum 317 supports a plurality of filter elements, anarrangement shown more clearly in FIG. 4B, and plenums 317 are closedfrom the inlet stream with a partition 316. The filter elements aresupported from lateral movement with a support structure 315. Thesupport provided to the element by partition 316 is in compression.Particulate matter collected on the surface of the filter elements isremoved from the surface of the filter, falls between the clean airplenums at 319, and is collected in the device 306 and removed at 307.The arrangement allows for a flow of gas to exit at 311 from the bottomof the filter, that is, below the elements. This allows for theinstallation of this filter in line with the existing gas flow from theexhaust duct of some types of kiln systems using cyclone preheaters, andis an advantage in retrofit applications. By employing the arrangementof FIGS. 4A and 4B, the ID fan can be closer to the tower, and thesupport of the elements is such that a longer element could be used.Overall, this would allow for the tallest and skinniest installation,allowing for the easiest retrofit in many installations. Pressuremonitoring device 308 monitors the difference in pressures attainedacross the partition between the clean and dirty sides of the filter.The temperature of the gas stream is monitored at 309 The cleaned gases311 in the chambers or plenums are removed from the catalytic filter viaa duct 310.

FIG. 4B depicts an isometric view of the embodiment depicted in FIG. 4A,with similar numbers depicting similar elements. Process gases 301 fromthe exit of the kiln installation, such as the exit of a cement kiln,preheater, or precalciner system or a lime kiln or preheater system aredirected via a conduit 302 to the catalytic filter unit 303. The filterunit features a number of filter elements 304 supported on a series ofchambers or plenums closed from the inlet stream with a partition 316.The filter elements are supported from lateral movement with a supportstructure 315. Particulate matter collected on the surface of the filterelements is removed at 307. The cleaned gases 311 in the chambers orplenums are removed from the catalytic filter via a duct 310.

FIG. 5 shows a similar system as depicted in FIG. 1, but utilizes thecatalytic filter system 100 in place of the main dust collector 80 shownin FIG. 1. In FIG. 5, similar numbers to those of FIG. 1 depict similarelements. This arrangement offers the advantage that the use ofpollution control equipment is minimized, as the catalytic filter systemis used as the main dust collector, which in turn reduces theinstallation and operational costs as well as power consumption. The useof this arrangement is more difficult to implement in that the operatingtemperatures of the incoming gas stream are typically lower than theoperating temperatures found nearer to the exit of the kiln or preheatersystem. This arrangement is preferred when the primary emissions thatthe catalytic filter system is intended to destroy can be effectivelyreduced in the temperature range found in this location. As analternative, a hot gas source 95, such as a portion or all of the gasstream leaving the cooler vent and removed from gas stream 7, betweenheat exchanger 8 and dust collector 9, or from the stack gas 11, may beused to return the gas temperature to a higher range which will improvethe activity of the catalytic filter system. The use of waste heat fromthe cooler vent system is preferred in that dust collector 9 may also beeliminated in whole or reduced in size if sufficient gas flow iscontinuously removed from this location, further reducing installationand operational costs as well as system power consumption.

FIG. 6 shows an example set of organic compound reduction curvescomparing the removal efficiency of a catalytic filter system operatedat varying temperatures for different examples of organic compounds fora catalytic filter system of the invention. The catalyst in use exhibitsgreater than 90% destruction of methanol at temperatures ranging between100 and 225° C., increasing rates of toluene removal from less than 30%at approximately 120° C. to greater than 90% destruction aboveapproximately 200° C., increasing rates of heptanes destruction rangingfrom less than 50% at approximately 160° C. to greater than 90% aboveapproximately 240 ° C., and increasing propane removal from 20% at 300°C. to greater than 60% at approximately 370° C. In laboratory testing,generation of these hydrocarbon reduction curves is achieved through thepassage of a carrier gas of similar composition to the gas streamexiting a cement or minerals processing system containing carbondioxide, water vapor, nitrogen, and oxygen, as well as typicalparticulate matter in set concentrations, and introducing knownquantities of hydrocarbons into the gas stream. Measurements takenbefore and after the catalytic filter system are used to determine thepercentage of incoming organic compound that is destroyed within thecatalytic filter system. Varying the temperature of the gas stream inthe catalytic filter system provides data for the generation of thereduction curve with regard to temperature. Organic compound reductioncurves such as that depicted in FIG. 6 will vary with the selection ofthe catalytic elements used in the production of the filter elementsutilized in the catalytic filter system, as well as any reactive agentsutilized in conjunction with the catalytic filter elements. Knowledge ofthe constituent organic compounds in the cement or minerals kiln orcalciner exhaust gas, through direct measurement or previouslyestablished predictive means, in comparison to organic compoundreduction curve with regard to operating temperature, can be utilized toselect the location and specific design configuration of the catalyticfilter system as depicted in FIGS. 1 through 5, or in similarvariations. As an example, the control of a process gas streamcontaining high levels of methanol and toluene may more efficientlyutilize the catalytic filter system as depicted in FIG. 5 and FIG. 6,while the control of a process gas stream containing high levels ofpropane may more efficiently utilize the catalytic filter system asdepicted in FIG. 1 and FIG. 6.

Using this invention, the exhaust gases from an industrial plant such asa cement or mineral kiln can be treated to reduce or destroy organiccompounds and other pollutants from the exhaust until the total contentof organic compounds and other pollutants in the gas stream is belowlevels that may be considered safe for release to the atmosphere.Treatment of the gas stream may also allow for removal of otherpollutants, or additional treatment downstream.

The invention having been thus described it will be obvious that thesame may be varied in many ways without departing from the spirit andscope thereof. All such modifications are intended to be included withinthe scope of the invention which is defined by the following claims.

We claim:
 1. A method for the reduction of contaminant emissionsincluding organic compounds present in vapor form from the process gasesof an industrial plant utilizing a kiln and/or calciner to heat treat araw material, said method comprising (i) directing plant process gascontaining entrained particulate matter and contaminant emissions fromthe plant to a pollution control device comprising a process gas inletand process gas outlet and an interior portion located intermediate theinlet and outlet, said interior portion containing at least onefiltering element for removing the particulate matter from the gas, saidat least one filtering element containing at least one catalyst forremoving some of the contaminant emissions; (ii) directing the processgas through the inlet and thereafter through the filtering element,wherein entrained particulate matter is separated from the process gasand the process gas comes in contact with the at least one catalyst tothereby reduce the contaminant emissions contained in the gas ; and(iii) directing cleaned process gas through the outlet of the pollutioncontrol device.
 2. The method of claim 1 further comprising: removingthe separated particulate matter from the pollution control device. 3.The method of claim 1 wherein the process gas is comprised of at leastone of kiln off gas, preheater off gas, precalciner off gas, rawmaterial milling system off gas, solid fuel milling system off gasproduct cooler vent gases and kiln process product milling off gases. 4.The method of claim 3 wherein the process gases comprise product coolervent gases.
 5. The method of claim 1 wherein the process gases withinthe pollution control device are maintained at a temperature between 80°C. and 450° C.
 6. The method of claim 1 wherein the at least onecatalyst is selected from the group comprising vanadium, platinum,palladium, ruthenium, titanium, lanthanum, cerium, yttrium, zirconium,tungsten, manganese, niobium, molybdenum, nickel, iron and copper. 7.The method of claim 1 wherein the filtering element is a fiberglass bag.8. The method of claim 1 wherein the filtering element is treated with amembrane.
 9. The method of claim 1 wherein the filtering element is aporous ceramic structure.
 10. The method of claim 1 wherein at least onereactive agent is contacted with the at least one catalyst agents toincrease the reduction of hydrocarbons present in the filteringelements.
 11. The method of claim 10 in which the at least one reactiveagent is selected from the group comprising ozone, peroxide, potassiumpermanganate, calcium chloride, sodium hydroxide, sodium bromide,bromine and chlorine.
 12. The method of claim 2 wherein removal of theseparated particulate matter from the pollution control device isachieved by pulsing gas through the filtering elements.
 13. The methodof claim 2 wherein removal of the separated particulate matter from thesurface of the filtering elements is achieved through sonic orultrasonic vibration.
 14. The method of claim 2 wherein removal of theseparated particulate matter from the surface of the filtering elementsis achieved through mechanical removal of particulate matter with asolid object.
 15. The method of claim 2 further comprising: returningthe removed particulate matter to the industrial plant process.
 16. Themethod of claim 1 in which the organic compounds comprise TotalHydrocarbons.
 17. The method of claim 1 wherein the organic compoundscomprise at least one of formaldehyde, acetaldehyde, xylene, benzene,styrene, and naphthalene.
 18. The method of claim 1 wherein the organiccompound comprise Volatile Organic Compounds.
 19. The method of claim 1in which mercury compounds within the process gas are oxidized by the atleast one catalyst.
 20. The method of claim 1 wherein at one of nitrogenoxides, dioxin/furan emissions and carbon monoxide are reduced by the atleast one catalyst.
 21. The method of claim 1 further comprisinginjection of a sorbent upstream of the pollution control device for theadsorption of at least one of sulfur dioxide, sulfur trioxide, arsenic,thallium, mercury, hydrogen chloride, hydrogen fluoride, or hydrogenbromide.
 22. The method of claim 21 wherein the sorbent includes atleast one of calcium oxide, calcium hydroxide, trona, sodiumbicarbonate, cement kiln dust, calcined material, and activated carbon.23. The method of claim 19 wherein a nitrogenated agent is introduced toincrease the reduction of nitrogen oxides.
 24. The method of claim 23wherein the nitrogenated agent includes at least one of ammonia, urea,ammonium bisulfate, or flyash.
 25. The method of claim 1 furthercomprising injection of a sorbent downstream of the pollution controldevice for the adsorption of at least one of sulfur dioxide, sulfurtrioxide, arsenic, thallium, mercury, hydrogen chloride, hydrogenfluoride, or hydrogen bromide.
 26. The method of claim 25 wherein thesorbent includes at least one of calcium oxide, calcium hydroxide,trona, sodium bicarbonate, cement kiln dust, calcined material, andactivated carbon.